Note: Descriptions are shown in the official language in which they were submitted.
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FAULT-TOLERANT MULTI-POINT FLAME SENSE CIRCUIT
FIELD OF THE INVENTION
[0001] This invention relates generally to burner flame sense
circuits°y, and more
particularly to electronic flame sense circuitry having multiple flame seruse
electrodes for
sensing multiple burners.
BACKGROUND OF THE INVENTION
[0002] Advances in the sophistication and reliability of control electronics
have long
made their incorporation in consumer appliances desirable. However, only
recently has the
cost of such electronics been compatible with the extremely competitive
marketplace for
these appliances.
[0003] One such commercial and consumer market into which control electronics
have
now been widely incorporated is that for consumer and commercial cooking
appliances
such as ovens. The control electronics for such modern ovens provide
programmable
cooking cycles and control each aspect of the flame control system,
prirraarily safety control.
Many such modern ovens incorporate a gas distribution system GDS) that
includes an
ignition module, solenoid valves, burners, and hot surface igniter or spark
electrodes. The
ignition module dispenses with the necessity of continually having a pilot
flame burning in
the appliance to reliably ignite the gas burners when called for by the
thermostat. The
electronically controlled solenoid valve controls the gas flow for each
cooking cycle, and
allows for proper purging and gas shutoff during fault conditions. Such ;gas
distribution
systems typically include an electronic flame sense circuit to sense when the
burners are
ignited. This flame sense is used to control the direct spark ignition of tl~e
gas and to sense
failure or flameout conditions. These conditions may necessitate reactivating
an ignition
sequence in an attempt to relight the burners or shutting off of the gas
solenoid valve to
allow for oven cavity purging before re-ignition is attempted. Electronic
flame sense
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2
circuits typically rely on a physical phenomena of flame known as currewt
rectification
within a flame. According to this principle, a flame will conduct electricity
in one direction.
As such, the flame may be modeled as a resistor diode combination that allows
current flow
only in a single direction therethrough. These circuits are, of course,
designed such that
they are fail safe. That is, the typical failure mode of these circuits is
such to indicate to the
electronic controller that no flame is sensed. In this way, the electronic
controller will shut
off the gas solenoid valve to the oven burners.
[0004) In typical consumer ovens, at least two burner elements are included
within the
oven cavity. Typically, a bottom burner is used during bake cycles, while an
upper burner
is used to allow broiling. In such applications, a need exists for flame
sensing of both the
upper and lower burners. While separate flame sense circuits could be
Lutilized, such would
serve to simply increase the cost of the sensing circuitry required by a
factor of two.
Indeed, in applications where multiple burners are used, the provision of
multiple flame
sense circuits increases the cost of the circuitry accordingly.
[0005] Recognizing that the two-burner configuration in a consumer oven allows
operations of only one burner at a time, i.e., either baking or broiling, a
single dual flame
sense circuit integrating two flame sensors has been developed as illustrated
in Fig. 1.
Under typical operating conditions, only one of the two flame sense electrodes
100, 102
would be required to sense flame at any given point in time based on the
alternate controlled
operation of the bake and broil burners. The flame-sensing portion of this
circuit is
powered from the line voltage L1 through a capacitor 104. Each flame sense
electrode 100,
102 also includes a current limiting resistor 106, 108. A voltage divider
network including
resistor 110, and the RC combination of resistor 112 and capacitor 114 i;>
also included.
The midpoint between this resistor 110 and the RC combination 112, 114 is
coupled
through resistor 1 I5 to the gate of a I 16 of a junction field effect
transistor (3FET) 118,
whose drain is coupled through resistor 120 to a 5 volt DC input and whose
source 122 is
coupled to ground.
[0006] With no flame present at either burner being sensed by sensing
electrodes 100,
102, operation of the flame sense circuit of Fig. 1 generates an output
vo:Ltage level equal to
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the drain to source voltage which is sensed by the electronic controller (not
shown) as a no
flame condition. That is, current flow during the positive half cycle of
source L 1 flows
through capacitor 104 resistor 110 and the RC network 112, 114. This generates
a positive
gate source voltage vDS. With such a positive voltage at gate 116, the JFET
118 remains in
a conducting state allowing current flow therethrough. During the negative
half cycle of
source L1, current flows from ground through the RC network, 112, 114, through
resistor
110 and capacitor 104 to the source L1. During this negative half cycle., the
voltage
developed at the gate 116 across the RC network 112, 114 is negative. This
negative
voltage, however, is not sufficient to pinch off the JFET 118 to halt current
flow
therethrough. As a result, the JFET 118 will remain on, and the controller
will continue to
sense a very small voltage vDS.
[0007] If a flame is present at either burner as sensed by electrodes 100,
102, the flame
sense circuit may be represented as illustrated in Fig. 2. As may be seen from
an analysis of
this Fig. 2, a flame may be represented as a series combination of a resistor
124 and a diode
126. As will be understood by those skilled in the art, the flame provides
rectification
whereby current flow is allowed only in a single direction therethrough.
During this flame
sense condition, current flow will be from source L1 through capacitor 104 to
a current
divider network comprised of resistor 106 and flame (resist:or 124 and diode
126), and the
voltage divider network of resistor 110 and RC network 112, 214. However, the
resistor
106 is sized in relation to resistor 110 to allow a majority of the current
flow from source Ll
during this positive half cycle through its branch of the circuit.
[0008] During the negative half cycle, however, the rectification action of
the flame
prevents any reverse current flow through resistor 106 of the circuit.
Instead, all of the
current flow during the negative half cycle flows from ground through tree RC
network 112,
114 through resistor 110 and capacitor 104 to source L 1. A,s a result of the
unequal current
flow through the RC network 112, 114 during the positive and negative half
cycles of
source Ll, an accumulation of negative charge is developed across capacitor
114. This
negative charge is coupled to gate 116 of JFET 118, which pinches off the JFET
118 halting
current flow therethrough. Because this negative charge is not drained away
during the
positive half cycle, the JFET 118 remains in an off condition during the
entire period of
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4
flame presence. This will be sensed as a constant 5 voltage level by the
electronic
controller, which will be read as a flame present condition. As soon as the
flame (resistor
124 and diode 126) disappears, operation of the circuit will return to that
illustrated and
described above with reference to Fig. 1, allowing the JFET 118 to turn on and
dropping the
sensed voltage flow a high level (e.g. 5v) to a low level (e.g. vDS.).
[0009] While the circuit of Fig. 1 provides a significant cost savings over
the usage of
two separate flame sense circuits, a passive failure at one of the flame sense
electrodes may
go undetected and result in a failure to sense flame when actually present.
Such a condition
is illustrated in Fig. 3. If one of the flame sense electrodes 102 is shorted
128 to ground, the
circuit will no longer sense flame at either of the flame sense electrodes
100, 102. When
neither the oven nor the broiler is turned on, the circuit appears to operate
normally with the
JFET 118 remaining in its conducting mode allowing current to flow
therethrough. As a
result, the presence of this short 128 will go undetected until one of the
burners is turned on.
Fig. 3 illustrates the effect when the burner associated with the other flame
sense electrode
100 is turned on.
[0010] During the positive half cycle of source Ll, current flows through
capacitor 104
into a three-way current divider network having one branch through the
unfaulted flame
sense electrode 100, another branch through the faulted electrode 102 anal
short 128, and a
third branch through the resistor 110, RC network 112, 114. During the
negative half cycle
of source L1, no current can flow through the sensed flame (resistor 124 diode
126) as
discussed above. However, instead of forcing the current to flow through the
RC network
112, 114 to develop a net negative charge across capacitor 114 thus pinching
off JFET 118,
reverse current is allowed to flow through the short 128. Due to the presence
of this short
128, sufficient negative charge across capacitor 114 cannot develop at the
gate 116 of JFET
118. As a result, the JFET 118 is allowed to remain in its conducting state,
which is sensed
by the electronic controller as a no-flame condition. As a result, the
electronic controller
will shut down the burner even though its flame sense electrode 100 is
unfaulted.
[0011] 'This operation may be understood more clearly With reference to Fig.
4. In this
Fig. 4, the flame sense circuit is redrawn to illustrate circuit operation
during a negative half
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cycle of source L1. To simplify the description of this circuit, the flame
sense electrode 100
is not shown because no current may flow in this branch during the negative
half cycle due
to the flame rectification. As may be seen more clearly from this redrawn
circuit of Fig. 4,
current during this negative half cycle will flow from ground through short
128, resistor
108, capacitor 104 to the source L 1. Current will also flow from ground
through the RC
network 112, 114, resistor 110, and capacitor 104 during this negative half
cycle. However,
the proportion of current flowing through the short circuit 128 to that
flowing through the
RC network 112, 114 is such that the charge across capacitor 114 at gate; 116
is not
sufficient to shut off switch 118. As such, the ~FET 118 is allowed to remain
conducting,
which is sensed as a no-flame condition.
[0012] As a result of this cross-contamination, field service personnel will
have a
difficult time isolating the failure. This is because the typical problem
report will indicate
that the burner with the unfaulted flame sense electrode 100 was turned on but
the system
did not sense a flame. However, examination of the flame sense electrode 100
will not
reveal any failure because, in fact, this electrode is not faulted. The cross
contamination of
failures in this circuit tends to increase the field service time required to
diagnose and
correct the problem, thus increasing the cost of ownership of the appliance
and leading to
customer dissatisfaction. However, the cost of utilizing two separate flame
sense circuits
for each of the two burners is cost prohibitive from a
manufacturing/marketability
standpoint. Therefore, a need exists in the art far a new and improved m.ulti-
point flame
sense circuit that does not suffer from the flame sense electrode failure
cross contamination
problem existing with the present circuit.
[0013] The invention provides such a circuit. These and other advantages of
the
invention, as well as additional inventive features, will be apparent from the
description of
the invention provided herein.
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6
BRIEF SUMMARY OF THE INVENTION
[0014] In view of the above it is an objective the present invention to
provide a new and
improved mufti-point flame-sensed circuit. More particularly, it is an
objective the present
invention to provide a new and improved mufti-point flame-sensed circL~it that
does not
suffer from the cross-contamination problem of the prior integrated mufti-
point flame sense
circuit discussed above. Specifically, it is an objective of the present
invention to provide a
full-tolerant mufti-point flame sensed circuit that allows a number of flame-
sense electrodes
to be utilized to sense multiple burners or multiple locations on a burner to
verify proper
operation of the burner element. Preferably, a failure of any one of the
multiple flame-sense
electrodes will not disrupt the ability of the circuit to properly sense flame
present at a non-
faulted flame-sense electrode.
[0015] In one embodiment of the present invention, each individual flame-sense
electrode is coupled to the mufti-point fault-tolerant flame-sense circuitry
of the present
invention via a separate channel powered by the line voltage and coupled to
the output
switching device. Preferably, each channel provides a capacitive couplialg to
the source
voltage, and a resistive coupling to the input-switching device. In a highly
preferred
embodiment, each of the channels for the multiple flame-sense electrodes are
coupled in
parallel with one another between these two points. A current limiting
resistor is also
included in association with each flame-sense electrode. The circuit elements
are then
balanced to ensure that proper operation of the sense circuit is not affectf;d
by failure of any
one of the flame-sense electrodes.
[0016] In one embodiment of the present invention, a fault-tolerant mufti-
point flame
sense circuit comprises an electronically controllable switch having a control
input, an RC
network having a first node coupled to the control input of the switch and a
second node
coupled to ground, and a number of flame sense electrode channels. Each flame
sense
electrode channel has a separate capacitive coupling to a line voltage input
and a separate
resistive coupling to the RC network. Preferably, each flame sense electrode
channel
includes a current limiting resistor that couples a flame sense electrode to a
junction
between the capacitive coupling to the line voltage input and the resistive;
coupling to the
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7
RC network. The flame sense electrode channels are preferably balanced with
one another
such that current flow between the line voltage input and the ground during
both positive
and negative half cycles of an external line voltage is equal when no flame is
present at any
of the flame sense electrodes. As such, the electronically controllable switch
remains in a
quiescent state when no flame is present at any of the flame sense electrodes.
[0017] In a further embodiment, each of the flame sense electrode cl'annels
for which
its associated flame sense electrode is not failed provides a current flow
path between the
line voltage input and the first node of the RC network. As such, a transition
of the
electronically controllable switch from a quiescent state is precluded without
a flame being
present at one of the flame sense electrodes of one of the channels for which
its associated
flame sense electrode is not failed when one of the flame sense electrode
channels includes
a flame sense electrode that is failed. Preferably, current flow through the
RC network is
unbalanced during positive and negative half cycles of the external line
voltage when one of
the flame sense electrode channels for which its associated flame sense
electrode is not
failed senses a flame: This results in a net voltage buildup across the RC
network and
transitions the electronically controllable switch from the quiescent state.
In one
embodiment, the flame sense electrode channels are balanced with one another
such that
current flow between the line voltage input and the ground during negative
half cycles of an
external line voltage is equal when flame is present at any of the flame sense
electrodes.
This results in a negative charge developing across the RC network. As a
result, the
electronically controllable switch changes from a quiescent state when flame
is present at
any of the flame sense electrodes.
[0018] In an alternate embodiment of the present invention, a fault-tolerant
mufti-point
flame sense circuit comprises a line voltage input adapted to receive AC line
voltage from
an external source, an electronically controllable switch, a switch control
circuit coupled to
the electronically controllable switch, and a number of parallel flame sense
channels. Each
flame sense channel is coupled between the switch control circuit and the line
voltage input.
Preferably, each flame sense channel comprises a flame sense electrode i.n
series with a
current limiting resistor that is coupled to a first capacitor, which is
coupled to the line
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8
voltage input. The current limiting resistor further is coupled to a first
resistor, which is
coupled to the switch control circuit.
(0019] In a further embodiment, the switch control circuit comprises a second
resistor
and a second capacitor coupled in parallel to ground. Preferably, the number
of parallel
flame sense channels comprises two parallel flame sense channels. Current flow
through
the parallel flame sense channels ensures that the switch control circuit
transitions the
electronically controllable switch when one of the flame sense channels senses
a flame. In
this embodiment, when at least one of the parallel flame sense channels
includes a flame
sense electrode that is shorted to ground, current flow through the other
parallel flame sense
channels ensures that the switch control circuit transitions the
electronically controllable
switch when one of the other flame sense channels senses a flame. The current
flow
through the other parallel flame sense channels ensures that the switch
control circuit does
not transition the electronically controllable switch when no one of the other
flame sense
channels senses a flame.
[0020] In yet a further embodiment of the present invention, a flame sense
circuit
comprises a first flame sense electrode coupled through a fnrst resistor to a
first node. This
first node couples a first capacitor and a second resistor, the first
capacitor being coupled to
a line voltage input and the second resistor being coupled to a flame sense
input node. The
flame sense input node is coupled to a third resistor that is coupled to a
gate of a junction
field effect transistor. The drain of the JFET is coupled through a resistor
to a control
voltage input, and its source is coupled to ground. The flame sense input node
further is
coupled to a fourth resistor and to a second capacitor, both of which are also
coupled to
ground. The circuit further includes a second flame sense electrode coupled
through a sixth
resistor to a second node coupling a third capacitor and a seventh resistor.
The third
capacitor is coupled to the line voltage input and the seventh resistor is
coupled to the flame
sense input node..
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BRIEF DESCRIPTION OF THE DRAW1NGS
[0021] The accompanying drawings incorporated in and forming a part of the
specification illustrate several aspects of the present invention, and
together with the
description serve to explain the principles of the invention. In the drawings:
[0022] FIG. 1 is a simplified circuit diagram of a prior mufti-point flame
sense circuit;
[0023] FIG. 2 is a simplified circuit diagram of the circuit of FIG. I
modeling the
sensing of a flame;
(0024] FIG. 3 is a simplified circuit diagram of the circuit of FIG. 1
modeling the
sensing of a flame and a failed flame sense electrode;
[0025] FIG. 4 is a redrawn simplified circuit diagram of the circuit of FIG.
3;
[0026] FIG. 5 is a simplified circuit diagram of an embodiment of the fault-
tolerant
mufti-point flame sense circuit of the present invention;
[0027] FIG. 6 is a simplified circuit diagram of the circuit of FIG. 5
modeling the
sensing of a flame;
[002g] FIG. 7 is a simplified circuit diagram of the circuit of FIG. 5
modeling the
sensing of a flame and a failed flame sense electrode;
[0029] FIG. 8 is a redrawn simplified circuit diagram of the circuit of FIG.
7.
[0030] While the invention will be described in connection with certain
preferred
embodiments, there is no intent to limit it to those embodirraents. On the
contrary, the intent
is to cover all alternatives, modifications and equivalents as included within
the spirit and
scope of the invention as defined by the appended claims.
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DETAILED DESCRIPTION OF THE INVENTION
[0031] To avoid the cross-contamination failure problem of the prior mufti-
point flame
sense circuit without increasing the cost significantly over the prior
circuit, the circuit of
Fig. 5 was developed. As will be described below, this circuit is immune from
cross-
contamination of a failure of one of the flame sense electrodes. That is,
while a failure of a
flame sense electrode for a particular burner will not allow that burner to
operate, other
burners within the system whose flame sense electrodes are not failed will be
able to
continue to operate properly. That is, their flame sense electrodes will
continue to properly
sense flame when present so that the electronic controller will operate those
burners and
their associated spark electrodes and gas solenoids correctly. This circuit
will also greatly
reduce the amount of time required to diagnose and repair a failure of one of
the flame sense
electrodes since the failure will be detected when the burner associated with
that failed
electrode is operated. In this way the field personnel will be able to
immediately inspect the
electrode of the suspect burner with confidence that a Latent failure located
elsewhere in the
system could not have caused the field problem. This greatly reduces the
amount of time
required for the service personnel, especially considering that the burners
and their
associated flame sense electrodes are physically located in different areas of
the oven
compartment. This reduces the overall cost of ownership and increases the
customer
satisfaction.
[0032) Turning now to the fault-resistant mufti-point flame sense circuit of
the present
invention illustrated in Fig. 5, it can be seen that, from a total part count
point of view, this
fault tolerant circuit adds only two passive components to the number of parts
required by
the flame circuit of Fig. l, which is subject to the cross-contamination
failure problem. As
such, its slight increase in cost over the prior circuit is far out weighed by
the reduce service
time and increased overall reliability provided by this circuit. It should be
noted that while
this circuit of Fig. 5 illustrates the usage of only two flame sense
electrodes 154, 152, one
skilled in the art will recognize that multiple flame sense electrodes may be
included in this
circuit as required by the particular installation into which it is to be
used! with appropriate
balancing of component values.
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[0033] In this improved circuit of Fig. 5, the line input L1 is coupled to
each of the
flame sense electrodes 150, 152 through different channels. The channel for
flame
electrode 150 utilizes capacitor 154, resistor 158, and is coupled through
resistor 169 to the
gate 170 of JFET 172 through resistor 164. For flame sense electrode 1:>2, the
channel
includes capacitor 156, resistor 160, and is coupled through resistor 169 to
the gate 170 of
JFET 172 through resistor 162. This resistor 169 is also coupled to an R.C
network
(including capacitor 166 and resistor 168) to ground. The source 176 of JFET
172 is also
coupled to ground, and the drain is coupled through resistor 174 to a 5 volt
supply. As may
be apparent from this description, additional flame sense electrodes may be
added to this
circuit by providing a capacitive coupling to source L1 and a resistive
coupling to the
resistor 169 and the gate 170 of JFET 172.
[0034] As may also be apparent from this Fig. 5, operation of this circuit
with no flame
present at any of these sensed burners results in JFET 172 remaining in its
conducting state
allowing current to flow therethrough. That is, the forward and reverse
current flow during
each of the positive and negative half cycles of source L 1 flows equally
through capacitors
154 and 156 and resistors 162 and 164 to the node coupled to the resistox 169
and gate 170,
and through the RC network 168, 166 to ground. As a result of this equal
forward and
reverse current flow, a sufficient negative charge cannot develop across
capacitor 166 to
pinch off JFET 172. As a result, the JFET 172 remains conducting and the
electronic
controller (not shown) senses a flame off or no-flame condition.
[0035] During a normal flame sense condition, the flame sense circuit of the
present
invention may be represented as illustrated in Fig. 6. In this Fig. 6, the
flame is represented
as resistor 124 and diode 126 coupling the flame sense electrode 150 to
ground. Current
flow during the positive cycle of source L1 will flow primarily through the
resistor 158,
flame sense electrode 150, and flame (represented by resistor 124 and diode
126) to ground.
While positive current will also flow through the RC network 166, 168, this
current will be
small as a result of the relative sizing of resistor 158 and 164. During thc~
negative half
cycle of source L1, current flow through flame sense electrode 150 is
precluded by the
rectification effect of the flame sensed thereby. As a result, all of the
reverse current flow
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12
during the negative half cycle of source L1 is forced to flow through the RC
network 166,
168 and is then divided equally between the paths including resistor 162 and
capacitor 156
and the path including resistor 164 and capacitor 154 to source L1. Sins~e the
proportion of
current flow through RC network 166, 168 during the negative half cycle is
much greater
than that flowing in the opposite direction during the positive half cycle., a
net negative
charge develops across capacitor 166. This net negative charge is applied to
gate 170 of
JFET 172, which pinches off the JFET 172 halting current flow therethrough.
The
electronic controller then senses that the JFET 172 has turned off, and
processes this
information as a flame present condition.
[0036] If a latent failure exists with one of the other flame sense electrodes
as illustrated
by the circuit of Fig. 7 as a short 128 from the flame sense electrode 152 to
ground, the
ability of the other flame sense electrodes to properly sense the presence of
flame at their
associated burners is not affected. Of course, the faulted flame sense
electrode 152 will not
be able to sense the presence of flame as a result of the short 128. As a a-
esult, the electronic
controller will not allow that associated burner to operate fur safety
reasons, and will
properly log a failure with regard to that burner.
[0037] Operation of this circuit with a flame sensed at flame sense electrode
150 and
with a failure 128 on an unassociated flame sense electrode 152 during the
positive half
cycle of source L 1 proceeds in much the same way as the unfaulted circuit in
Fig. 6. That
is, only a very small portion of the current from source L 1 us allowed to
:flow through the
RC network 166, 168 during this positive half cycle. The majority of the
current during this
positive half cycle flows instead through the two flame sense electrode
branches. While
more of the current flows through the faulted flame sense electrode 152 due to
the short
128, as opposed to the presence of the flame represented by resistor 124 and
diode 126, the
effect from the standpoint of the RC network is nearly the same, i.e. not
:much positive
current flows therethrough during the positive half cycle.
[0038] Operation of the fault-tolerant mufti-point flame sense circuit of the
present
invention during the negative half cycle of source L1 with a failure of an
unassociated flame
sense electrode 152 varies significantly from the prior mufti-point flame
sense circuit
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13
discussed above. Specifically, while current is allowed to flow through the
short circuit 128
of flame electrode 152 during the negative half cycle of source L1, a net
negative charge
across capacitor 166 is still generated sufficient to pinch off the current
flow through JFET
172. This allows the electronic controller to sense a flame condition at flame
sense
electrode 150.
[0039] During this negative half cycle of source L1, the circuit of Fig. 7 may
be redrawn
as illustrated in Fig. 8 to simplify the understanding of the operation of
this circuit. During
the negative half cycle of source Ll, the current will flow from ground
through the short
128 of flame sense electrode 152 and its associated resistor 160 through
capacitor 156 to
source L 1. Current will also flow from ground through the RC network 166, 168
through
resistor 162 and capacitor 156 to L1. However, current is also allowed to flow
through the
channel associated with the flame sense electrode 150, that is through
resistor 164 and
capacitor 154 to source Ll . As may be seen from a comparison of this Fig. 8
with the prior
circuit illustrated in Fig. 4, the addition of the extra channel for current
flow during the
negative half cycle (resistor 164, capacitor 154) allows a sufficient negative
charge to be
developed across capacitor 166 as coupled to gate 170 so that the JFET :172
may still be
pinched off, halting current flow therethrough. The electronic controller (not
shown) will
detect this as a flame present condition, which is proper because of the flame
present at
flame sense electrode 150. If no flame were present at this flame sense
electrode 150, there
would not be the unbalance current flow through the RC network 166, 168 that
will result in
a net negative charge being developed across capacitor 166 sufficient to pinch
off JFET
172. Only when the flame is present and current is allowed to flow through the
associated
unfaulted flame sense electrode 150 does this current flow unbalance result in
the
development of a charge sufficient to pinch off the switch 172.
(0040] In one embodiment of the present invention, the circuit is balanced as
follows:
capacitors 154 and 156 are 0.01 microfarads, resisters 158 and 160 are 1.0
megaahms,
resistors 162, 164, and 169 are 4.7 megaohms, resistor 168 is 22 megaohms, and
capacitor
166 is 0.1 microfarads. Preferably, the ratios of resistor 158 to resistor
162, and of resistor
160 to resistor 164 are equal and a minimum of 1 /4 to 1.
CA 02432519 2003-06-17
r,vn~solsos
14
[0041] The use of the terms "a" and "an" and "the" and similar referents in
the context
of describing the invention (especially in the context of the following
claims) are to be
construed to cover both the singular and the plural, unless otherwise
indiicated herein or
clearly contradicted by context. The terms "comprising," "having,"
"including," and
"containing" are to be construed as open-ended terms (i.e., meaning
"including, but not
limited to,") unless otherwise noted. Recitation of ranges of values herein
are merely
intended to serve as a shorthand method of referring individually to each
separate value
falling within the range, unless otherwise indicated herein, and each separate
value is
incorporated into the specification as if it were individually recited herein.
All methods
described herein can be performed in any suitable order unless otherwise
indicated herein or
otherwise clearly contradicted by context. The use of any and all examples, or
exemplary
language (e.g., "such as") provided herein, is intended merely to better
illuminate the
invention and does not pose a limitation on the scope of the invention unless
otherwise
claimed. No language in the specification should be construed as indicating
any non-
claimed element as essential to the practice of the invention.
(0042] Preferred embodiments of this invention are described herein, including
the best
mode known to the inventors for carrying out the invention. Variations of
those preferred
embodiments may become apparent to those of ordinary skill in the art upon
reading the
foregoing description. The inventors expect skilled artisans to employ such
variations as
appropriate, and the inventors intend for the invention to be practiced
otherwise than as
specifically described herein. Accordingly, this invention includes all
modifications and
equivalents of the subject matter recited in the claims appended hereto as
permitted by
applicable law. Moreover, any combination of the above-described elements in
all possible
variations thereof is encompassed by the invention unless otherwise indicated
herein or
otherwise clearly contradicted by context.
